Numerous anti-theft security devices already exist for motor vehicles, based on the general principle of a locking catch that is received in an associated recess in the steering column of the vehicle, level with a housing provided for the ignition key.
Nevertheless, such devices can be broken in the event of a break-in so that they no longer fulfill their security function. Even if they are not broken sufficiently to manage to unlock the steering column, damage is often caused to the steering column, to the steering wheel, and to the trim of the dashboard.
That is why designers have been led to consider systems that enable the steering wheel to be decoupled from the steering column.
Certain systems have thus been proposed in which the steering wheel can be decoupled from the steering column so as to release the steering wheel, as illustrated, for example, in the following documents: U.S. Pat. No. 1,809,765, FR-A-2 406 545, FR-A-2 545 431, and FR-A-2 584 353. Such systems nevertheless suffer from the drawback of requiring the steering wheel to be carried away, which is inconvenient.
Mention may also be made of systems that make use of erectile coupling studs which are moved under the control of an electric motor (e.g. as shown in Document FR-A-2 527 999). Such systems are nevertheless complicated and not very reliable; in addition, electrical control is not possible on all steering wheels, thereby limiting possible applications.
Document EP-A0 008 308 describes a device in which the steering column is made in two portions, one of which portions is designed to be removable or installable so that coupling between the steering column and the steering wheel can be interrupted or, on the contrary, re-established. Such a device nevertheless suffers from the drawback of requiring the steering column of the vehicle to be specially adapted, which is expensive. In addition, the device is not suitable for fitting rapidly and reliably.
Proposals have also been made to provide an anti-theft mechanism for a vehicle by removing a part of the anti-theft device, such removal automatically decoupling the steering wheel from the steering column. This state of the art is particularly well illustrated by the following documents: EP-A0 162 986, EP-A0 203 850, and EP-A-0 445 024.
The devices described in above-mentioned documents EP-A-0 162 986 and EP-A-0 203 850 rely on the general principle of an axial stack of parts coaxial with the steering column, and the user must extract from the stack a part that provides rotary coupling between its upstream and downstream ends in the stack. Such devices have the advantages of being relatively simple to design, but they require disassembly in order to enable the parts to be extracted (as in document EP-A-0 162 986) or else they require coupling means of more sophisticated design to be provided so that only one removable item needs to be disengaged such as a pin having retractable balls (as in document EP-A-0 203 850).
In a variant of the above-mentioned devices, proposals have recently been made for an off-axis mount enabling the steering wheel to pivot about an axis parallel to the steering column but offset therefrom: a laterally disposed removable part provides coupling with the steering column when in place and enables decoupling to be achieved when it is removed to be taken away (leaving the steering wheel rotating on its off-axis mount). Such a system is nevertheless relatively vulnerable insofar as the removable part is directly accessible, thereby enabling it to be tampered with: in addition, the mount runs the risk of being jammed if it is too tight.
The state of the art is also illustrated by Documents U.S. Pat. No. 4,924,685 and EP-A-0 402 938, which describe mechanisms in which a portion associated with the steering wheel is displaceable along the axis of the steering column by direct coupling (using a cam or a rack) with the cylinder of a lock.
An object of the invention is to provide a security device which is more effective than the above-mentioned system with respect to security, and reliability, and also ease of use.
Another object of the invention is to provide an anti-theft security device equally capable of being installed on initial assembly (during manufacture) or as a retrofit (by altering items that already exist, thereby equipping a vehicle with the security device).